ISOFORMS AND SPLICE VARIANT OF TRANSFORMING-GROWTH-FACTOR BETA-BINDING PROTEIN IN RAT HEPATIC STELLATE CELLS

Background & Aims: Hepatic stellate cells (HSCs) are one important sou rce for transforming growth factor beta (TGF-beta). They produce TGF-b eta in a latent form associated with latency-associated peptide and la tent TGF-beta-binding protein (LTBP), This study was designed to inves tigate, on RNA and protein levels, which isoforms of LTBP and TGF-beta are expressed in HSCs and myofibroblasts. Methods: HSCs isolated from rat liver were analyzed for LTBP and TGF-beta at various times of cul ture during transdifferentiation into myofibroblasts using immunocytoc hemical staining, metabolic labeling and immunoprecipitation reverse-t ranscription polymerase chain reaction (RT-PCR), and sequencing, Resul ts: Alkaline phosphatase-anti-alkaline phosphatase staining and fluore scence immunostainings indicated the expression of all three component s of the large latent TGF-beta complex in HSCs and myofibroblasts. Tra nscripts of three TGF-beta and LTBP isoforms were detected by RT-PCR a nd confirmed by sequence analyses. A new LTBP-1 splice form was found lacking part of the hinge region with a potential proteinase cleavage site. Metabolic labeling followed by immunoprecipitation with LTBP ant iserum confirmed the synthesis and secretion of various LTBP-related p roteins. Conclusions: The existence of different LTBP isoforms and spl ice variants in HSCs and myofibroblasts suggests multiple functions of the LTBP family in rat liver, which might not be restricted to the ma intenance of TGF-beta latency.